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A large variety of gas phase conformations of the amino acids glycine, alanine, and cysteine is studied by numerically efficient semi-local gradient-corrected density functional theory calculations using a projector-augmented wave scheme and periodic boundary conditions. Equilibrium geometries, conformational energies, dipole moments, vibrational modes, and IR optical spectra are calculated from first principles. A comparison of our results with values obtained from quantum-chemistry methods with localized basis sets and nonlocal exchange-correlation functionals as well as with experimental data is made. For conformations containing strong intramolecular hydrogen bonds deviations in their energetic ordering occur, which are traced back to different treatments of spatial nonlocality in the exchange-correlation functional. However, even for these structures, the comparison of calculated and measured vibrational frequencies shows satisfying agreement.

We present equilibrium geometries, vibrational modes, dipole moments, ionization energies, electron affinities, and optical absorption spectra of the DNA base molecules adenine, thymine, guanine, and cytosine calculated from first principles. The comparison of our results with experimental data and results obtained by using quantum chemistry methods show that in specific cases gradient-corrected density-functional theory (DFT-GGA) calculations using ultrasoft pseudopotentials and a plane-wave basis may be a numerically efficient and accurate alternative to methods employing localized orbitals for the expansion of the electron wave functions., (Copyright 2003 Wiley Periodicals, Inc. J Comput Chem 1: 112-122, 2004)